As information technology develops, display devices become more and more important as an information delivery medium. In the display device field, demand for a large screen, a reduction in weight, a reduction in thickness, high image quality, and the like are growing in line with such technology development, and in order to meet the requirements, a liquid crystal display (LCD), as a substitute for a conventional cathode-lay tube (CRT), has been widely used.
An LCD generally includes a substrate on which pixels are formed in a matrix, an opposite substrate, and a liquid crystal material having dielectric anisotropy interposed between the two substrates. The LCD is operated such that an electric field is applied between the two substrates and the strength of the applied electric field is adjusted to control the amount of light that transmits through the liquid crystal material to thus display a desired image. More specifically, when voltage is applied to the liquid crystal through pixel electrodes provided in each pixel of the LCD, the arrangement of liquid crystal are changed accordingly. As light passes through the liquid crystal of the changed state, the light is diffracted to obtain a desired image. Since an LCD is not a self-emissive display device, a lamp installed on a rear surface thereof operates as a light source.
An LCD is required to support a dimming function for controlling brightness of the lamp in order to obtain high image quality while reducing power consumption when displaying video images. A method for controlling brightness of the lamp includes an analog method for changing the strength of current flowing across the lamp and a PWM method for changing an on/off duty ratio for the current flowing across the lamp while uniformly maintaining the strength of the lamp current.
Meanwhile, photosensitivity and fatigue of human beings vary according to the intensity of the illumination of the environment. For example, in an environment in which the intensity of illumination is low, like at nighttime, the human eye is sensitive to even a small amount of light, compared with a brighter environment, making the human eyes feel easily tired. A maximum brightness level of a display device which can be recognized by the human eyes in a dark environment has a value lower than that in a bright environment. Therefore, in the environment in which an external intensity of illumination is low, although the brightness of the display device is increased up to the same level as that of the environment in which the external intensity of illumination is high, the human eyes cannot recognize the brightness of a certain level or higher. Nevertheless, an excessive increase in the brightness of the display device would simply cause unnecessary energy consumption.
Consequently, a display device capable of adjusting the brightness of a light source such that the brightness can be changed to have levels within an appropriate range recognizable by the human eye according to the intensity of illumination of the environment, and a method for controlling the brightness of the light source thereof are required.